The new wind machines also have been mounted on pedestals, which increase the elevation. This elevation increases the efficiency of the wind machine on an average yearly output. The new generation of wind machines requires very little maintenance, i.e., about 2 times per year. Therefore, the machines can be mounted in remote locations and can operate trouble free for extended periods of time. Due to many political and human nature considerations, many wind machines are now being placed in offshore waters. The distance from the shoreline varies but from the human relations viewpoint, they are usually out of the sight of the land.
The generating systems can be sized between 1.5 megawatts and 3.5 megawatt machines with some wind turbines being operated at 250 kw. The generating systems including blades, gearboxes and control systems, have been proven and tested. The required towers to elevate the generator have also been proven and tested. The offshore oil and gas industries have proven throughout the world that offshore structures can be designed and installed to withstand the harshest atmospheric environment.
New techniques have been developed in the fabrication and installation of these structures. These techniques are useful in the practice of this invention in order to use the most efficient manner to construct, install and maintain offshore wind machines. It is also important to understand that the total cash flow from the wind power machine has a cap due to the sales price of electrical energy onshore. Consequently, the additional cost of installation in providing the structure is of paramount importance.
Offshore structures are designed to accommodate the soil bearing capacity of the sub bottom strata. In some cases, extremely soft bottoms were encountered in delta regions of the world. Also, some sub bottoms are hard rock or coral reef. Therefore, the anchoring system, which is required, varies greatly. Also, if wind machines are placed in hardy conditions, ice conditions are a consideration regarding the structural strength of the structure and materials. Consequently, soil borings are required to assure that the structure will have ample strength to accommodate the weight and overturning moment of the wind machine.
Another consideration is wave and wind conditions to which the structure is subjected. Therefore, the anchoring of the windmill structure will be different in different areas of the world. With all the variables and substantially unpredictable environments where the wind power generation is attempted, it is little under that post construction problems appear which affect the efficiencies of operation of the installations.
While the offshore support structure can be generally constructed as well known in the offshore oil industry and specifically as described in U.S. Pat. No. 4,260,291, two problems have generally developed in connection with the generation of the electric power at these offshore facilities. One such problem is vibration of the structure caused by the wind itself acting upon the structure and the rotation of the windmill blades to turn the generator to develop the electric power. A number of attempts have been made to combat these vibrations problems as described in U.S. Pat. No. 4,515,525 (minimization of the effects of yaw oscillation in wind turbines), U.S. Pat. No. 6,672,837 (wind turbine with an oscillation dampening means) and U.S. Pat. No. 6,695,588 (dampening of oscillations in wind turbines). U.S. Pat. No. 4,469,956 describes a support structure fitted between the windmill and the tower to reduce the communication of vibration from the blades and rotating turbine to the tower. While a number of attempts have been made to solve the vibration problem, much improvement could still be made.
Another problem exists with respect to the offshore windmill electric generators. After a period of time there often is a settling of one or more of the support members affecting the alignment of the structure such that the nacelle and axis of the generator and windmill cease to be level or horizontal. This settling is often exacerbated, if not caused, by the vibration of the tower supporting the windmill. This causes uneven forces to be present during operation creating additional wear and tear and resulting inefficiencies, if not a major reconstruction adjustment of the windmill involved.